1. Field of the Invention
The present invention generally relates to a cleaning device, a process cartridge, and an image forming apparatus, and more specifically to a cleaning device, a process cartridge, and an image forming apparatus having an electrophotographic process unit.
2. Description of the Related Art
The electrophotographic process performed in an image forming apparatus generally includes charging, exposing, developing, transferring, fixing, and cleaning. In the cleaning process performed as a final process, a blade cleaning method is usually used.
Some full-color image forming apparatuses employ the blade cleaning method. Such full-color image forming apparatus includes developing devices for developing yellow (Y), magenta (M), cyan (C), and black (Bk) images, respectively. Each developing device includes a photosensitive drum serving as an image carrier capable of being rotatably driven, and the surface of the photosensitive drum is uniformly charged by a charging device. Then, a laser beam is irradiated onto the surface by an optical system for exposure so that the surface of the photosensitive drum is exposed to form an electrostatic latent image on the surface of the photosensitive drum. Then, a developing agent in the developing unit is applied to the surface of the photosensitive drum so that a visible image is formed on the photosensitive drum.
The image forming apparatus further includes an intermediate transferring device, and the formed visible image is transferred in a contacting section between the intermediate transferring device and the photosensitive drum. More specifically, the formed visible image on the surface of the photosensitive drum is transferred onto a surface of a transfer belt by a transferring roller in the intermediate transferring device. The transferred developing agent forming the visible toner image is transferred onto a sheet serving as an image carrier in a secondary transferring section. Then, the sheet is fed into a fixing device, where the toner image is fixed on the sheet. On the other hand, the developing agent remaining on the surface of the photosensitive drum is cleaned and removed by a cleaning blade in a cleaning device. An image forming apparatus having the above configuration is described in Patent Document 1 (Japanese Patent Application Publication No. 2006-243411).
The cleaning blade accommodated in a developing device has a plate shape and is made of an elastic member of such material as polyurethane. The cleaning blade is fixed to a supporting body and is pressed to and in contact with a surface of the rotating photosensitive body. Generally, there are two types of developing units.
FIG. 13 is a cut-open view schematically showing a first type of the developing unit. As shown in FIG. 13, in this developing device 4, a head of a cleaning blade 11a of a cleaning device 11 is in contact with a photosensitive drum 1. The cleaning blade 11a is directly fixed to a chassis 4j of the developing device 4 with a bolt so that the cleaning blade 11a is pressed to and in contact with the photosensitive drum 1 with a prescribed contacting pressure. This contacting pressure is produced by a restoration force due to elastic deformation of the cleaning blade 11a, the restoration force being used as a blade pressing force applied to the photosensitive drum 1.
FIG. 14 is a cut-open view schematically showing a second type of the developing unit. As shown in FIG. 14, in the developing device 4, a pressure promoting member 4k includes a supporting shaft and a spring so that the pressure promoting member 4k is rotatably attached to a part of a supporting body of the developing device 4. As a result, the cleaning blade 11a is in contact with the surface of the photosensitive drum 1 due to a pressing force produced by the pressure promoting member 4k. 
The cleaning blade 11a fixed to the chassis 4j of the first developing unit 4 has some advantages: a simple structure, easy to reduce the size, and low cost because such units as a driving unit and a biasing unit are not necessary. However, since the cleaning blade 11a always in contact with the image carrier (photosensitive drum), the cleaning blade 11a is likely to be deformed and the pressure applied to the image carrier is likely to be reduced due to the permanent distortion of the cleaning blade 11a. Further, it is difficult to remove toner or any foreign matter such as paper powder remaining in a contacting part between the elastic cleaning blade 11a and the image carrier 1, which often causes abnormal images.
On the other hand, in the second developing unit 4, the movable cleaning blade 11a can be put in contact with and separated from the image carrier by an added contacting and separating mechanism for separating the cleaning blade 11a from the image carrier and a position controlling member for adjusting the position of the cleaning blade 11a with respect to the image carrier. This method is being employed in systems requiring long service life.
As described above, implementing such a movable cleaning blade or such a contacting and separating mechanism is useful to avoid damage to the edge of the cleaning blade caused by the residual toner or foreign matter. However, recently there has been a demand for reducing the size of the image forming apparatus. Unfortunately, it is difficult to achieve a good balance between the implementation and the demand because of cost increases with conventional technology. As a result, the implementation is tending to be neglected and long service lives of the cleaning blade and the photosensitive body are not being provided in many cases.